Spam is the use of electronic messaging systems to send unsolicited bulk messages indiscriminately to end users. Various forms of spam exist including email spam, instant messaging spam, and the like. A relatively new form of spam delivers messages to users of Voice over Internet Protocol (VoIP) telephony systems. This SPam over Internet Telephony (SPIT) is VoIP spam that typically uses the Session Initiation Protocol (SIP). Much like a traditional spam recording played on a traditional telephone system, SPIT initiates calls to VoIP users and, when the call is answered, typically plays a prerecorded spam message intended for the end user to hear. As the name implies, VoIP is a technology that provides for voice communications over Internet Protocol (IP) networks, such as the Internet. The proliferation of high speed network connections and the low relative cost of using VoIP has both increased the quality and the popularity of the technology. The Session Initiation Protocol (SIP) is a signaling protocol that is often used for controlling VoIP sessions. SIP can be used to create, modify, and terminate two-party or multi-party sessions. Spammers increasing use SIP to initiate sessions with VoIP users in order to deliver spam messages. VoIP technology is similarly popular to spammers as it is relatively inexpensive to deliver such spam messages. Because the messages travel over IP networks, rather than traditional telephone systems, the calls are not subject to most, if not all, traditional telephone system costs and fees, such as traditional long distance calling fees.